Rep. Cory Gardner outraises Sen. Mark Udall as voting begins in Colorado

Rep. Cory Gardner is outraising Democratic Sen. Mark Udall and has more than triple the incumbent's cash on hand in the final days of the campaign, according to reports from both sides of the race.

Gardner on Monday reported raising $1.28 million in the first two weeks of October and having $1.87 million cash on hand as of Oct. 15. Udall reported raising $735,000 and having $536,000 cash available.

Udall's campaign has argued that it has an advantage in the race's final days because it and its Democratic allies are scheduled to air more ads than Gardner and Republicans — a reflection of how Democrats were able to purchase air time earlier in the election, when it was cheaper. But Gardner's outsized edge in available cash gives his campaign flexibility in the stretch.

The reports provide the last glimpse of the two campaigns' financial situations in the closing days of one of the nation's priciest Senate contests. Last quarter, Gardner outraised Udall by $100,000, a rare event for a challenger. The congressman only began his campaign in March and has had far less time to raise funds than the incumbent.

The fundraising hauls also come as voting has already begun in Colorado. All voters were mailed ballots that can be sent in the mail or, starting Monday, dropped off at polling places around the state. Citizens will be able to register to vote until Election Day. The new voting laws were passed by the state's Democratic-controlled Legislature over Republican objections last year and are expected to help Udall, who has trailed in recent public polls.

Gardner and Udall are locked in a tight battle that could determine which party controls the U.S. Senate. Republicans need to net six seats to take over the chamber.